Its been on the front page of the Southern website for months. I doubt very much that regular commuters only ever depend on leaflets these days.
There are plently of posters out there so if you don't check, what else can be done? Employ people to pester everyone daily until it sinks in?
Your last point over staff who don't understand the railway is a fair one.
Im assuming you mean 1st September with this? Again there been stuff around about this too.
Completely untrue. Try this link. Or if you have a smartphone thery have an app.
http://www.southernrailway.com/your-journey/plan-your-journey/live-running-information/
There are a lot of commuters who don't use access via there PC to see this information - it is not acceptable to use Websites/Twitter as primary information points in these circumstances and I think this has been borne out as a lot of commuters are confused.
The posters and messages direct users to web sites rather than passing information. The revised timetable appeared on posters at Redhill Station on the Thursday evening before the closedown on Friday. There has been no information in advance to say that FCC services are withdrawn from Redhill for the week. (It appeared on FCC's website at the weekend)
Even the booklet you pointed out shows the wrong information and only gives off-peak services no detail of peak changes.
To be fair there has been a lot of posters and information available - but it has been so generic that most people haven't understood it and the detail on the website has been quite poor.
However I do accept that the information is there just not readily available. I think at major stations like Redhill having purple people explain the services a week or two before would have been helpful.
As for the services - finding 50% of the normal London service cut and all the replacement trains at 8 coach length instead of normal 12 coach trains has been a nightmare (at least in my part of the peak). However I think other routes have done better